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Why do flowers of a hummingbird-pollinated mistletoe face down?
Article first published online: 20 DEC 2001
DOI: 10.1046/j.0269-8463.2001.00580.x
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How to Cite
TADEY, M. and AIZEN, M. A. (2001), Why do flowers of a hummingbird-pollinated mistletoe face down?. Functional Ecology, 15: 782–790. doi: 10.1046/j.0269-8463.2001.00580.x
Publication History
- Issue published online: 20 DEC 2001
- Article first published online: 20 DEC 2001
- Received 22 January 2001; revised 6 July 2001; accepted 10 July 2001
- Abstract
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Keywords:
- Female and male reproductive success;
- flower orientation;
- hummingbird pollination;
- pollen tubes;
- rain
Summary
- 1Pendant flowers are common among hummingbird-pollinated plants. A downward orientation of the flower or inflorescence could represent an adaptation to avoid either flower flooding or direct pollen losses from anthers or stigmas under rainy conditions.
- 2We studied the adaptive significance of this trait experimentally in Tristerix corymbosus Kuijt (Loranthaceae), a mistletoe native to the temperate forests of southern South America. We applied three treatments: (i) natural pendant inflorescences; (ii) inflorescences tethered to face up; and (iii) inflorescences tethered to face down (as a control for tethering). We also considered natural exposure to rain as a second factor.
- 3The treatments did not differ significantly in either nectar volume or concentration. Flowers exposed to rain for most of their lives contained more diluted nectar than those that remained dry, but this result did not depend on either inflorescence or flower orientation.
- 4We found significantly fewer pollen tubes in styles of flowers from inflorescences tethered to face up than in flowers receiving the other two treatments, but this could not be attributed to a direct effect of rain exposure. Inflorescence orientation did not affect either the number of pollen grains left in anthers or seed set. No strong evidence was found for differential visitation by hummingbirds in relation to a flower’s angle.
- 5The results of this work support neither the flower-flooding nor the pollen-protection hypothesis. However, a flower’s orientation may affect the extent of within-flower self-pollination or the efficiency of pollen transfer from a hummingbird’s bill onto a flower’s stigma.